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Despite its importance in the large-scale synthesis of transition metal dichalcogenides (TMDC) molecular layers, the generic quantum effects on electrical transport across individual grain boundaries (GBs) in TMDC monolayers remain unclear. Here we demonstrate that strong carrier localization due to the increased density of defects determines both temperature dependence of electrical transport and low-frequency noise at the GBs of chemical vapor deposition (CVD)-grown MoS2 layers. Using field effect devices designed to explore transport across individual GBs, we show that the localization length of electrons in the GB region is -30-70% lower than that within the grain, even though the room temperature conductance across the GB, oriented perpendicular to the overall flow of current, may be lower or higher than the intragrain region. Remarkably, we find that the stronger localization is accompanied by nearly 5 orders of magnitude enhancement in the low-frequency noise at the GB region, which increases exponentially when the temperature is reduced. The microscopic framework of electrical transport and noise developed in this paper may be readily extended to other strongly localized two-dimensional systems, including other members of the TMDC family. [ABSTRACT FROM AUTHOR]

Transition metal dichalcogenide (TMD) alloys form a broad class of two-dimensional (2D) layered materials with tunable bandgaps leading to interesting optoelectronic applications. In the bottom-up approach of building these atomically thin materials, atomic doping plays a crucial role. Here we demonstrate a single step CVD (chemical vapor deposition) growth procedure for obtaining binary alloys and heterostructures by tuning atomic composition. We show that a minute doping of tin during the growth phase of the Mo1-xWxS2 alloy system leads to formation of lateral and vertical heterostructure growth. High angle annular dark field scanning transmission electron microscopy (HAADF-STEM) imaging and density functional theory (DFT) calculations also support the modified stacking and growth mechanism due to the nonisomorphous Sn substitution. Our experiments demonstrate the possibility of growing heterostructures of TMD alloys whose spectral responses can be desirably tuned for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

Monolayermolybdenum disulfide (MoS2) with a directband gap of 1.8 eV is a promising two-dimensional material with apotential to surpass graphene in next generation nanoelectronic applications.In this Letter, we synthesize monolayer MoS2on Si/SiO2substrate via chemical vapor deposition (CVD) method andcomprehensively study the device performance based on dual-gated MoS2field-effect transistors. Over 100 devices are studied toobtain a statistical description of device performance in CVD MoS2. We examine and scale down the channel length of the transistorsto 100 nm and achieve record high drain current of 62.5 mA/mm in CVDmonolayer MoS2film ever reported. We further extract theintrinsic contact resistance of low work function metal Ti on monolayerCVD MoS2with an expectation value of 175 Ω·mm,which can be significantly decreased to 10 Ω·mm by appropriategating. Finally, field-effect mobilities (μFE) ofthe carriers at various channel lengths are obtained. By taking theimpact of contact resistance into account, an average and maximumintrinsic μFEis estimated to be 13.0 and 21.6 cm2/(V s) in monolayer CVD MoS2films, respectively. [ABSTRACT FROM AUTHOR]

Monolayer molybdenum disulfide (MoS2) is a two-dimensionaldirect band gap semiconductor with unique mechanical, electronic,optical, and chemical properties that can be utilized for novel nanoelectronicsand optoelectronics devices. The performance of these devices stronglydepends on the quality and defect morphology of the MoS2layers. Here we provide a systematic study of intrinsic structuraldefects in chemical vapor phase grown monolayer MoS2, includingpoint defects, dislocations, grain boundaries, and edges, via directatomic resolution imaging, and explore their energy landscape andelectronic properties using first-principles calculations. A richvariety of point defects and dislocation cores, distinct from thosepresent in graphene, were observed in MoS2. We discoverthat one-dimensional metallic wires can be created via two differenttypes of 60° grain boundaries consisting of distinct 4-fold ringchains. A new type of edge reconstruction, representing a transitionstate during growth, was also identified, providing insights intothe material growth mechanism. The atomic scale study of structuraldefects presented here brings new opportunities to tailor the propertiesof MoS2via controlled synthesis and defect engineering. [ABSTRACT FROM AUTHOR]

Here, we design and develop high-power electric double-layercapacitors(EDLCs) using carbon-based three dimensional (3-D) hybrid nanostructuredelectrodes. 3-D hybrid nanostructured electrodes consisting of verticallyaligned carbon nanotubes (CNTs) on highly porous carbon nanocups (CNCs)were synthesized by a combination of anodization and chemical vapordeposition techniques. A 3-D electrode-based supercapacitor showedenhanced areal capacitance by accommodating more charges in a givenfootprint area than that of a conventional CNC-based device. [ABSTRACT FROM AUTHOR]